To develop and refine techniqqes fkr the axenic cultivation of Entamoeba histolytica, related amebae and other parasitic protozoa; to define their in vitro nutritional requirements, to study their metabolism, and mechanisms of pathogenicity. To study naturally occurring viruses of E. histolytica: elucidation of the relationships between Entamoeba histolytica and its indigenous viruses, determination if any, of the relationships between amebal virus and virulence of the amebae, histo-pathological study of hepatic amebiasis in the hamster and bird. To develop techniques for cryopreservation of parasitic protozoa, to study mechanisms involved in resistance of these organisms to freezing injury.